Isolation valves are a common valve type for isolating adjacent portions of a fluid pathway. A common configuration of an isolation valve is a ball valve that is rotatable between a closed position for blocking fluid flow, and an open position for permitting fluid flow between the adjacent portions of the fluid pathway. An exemplary use of a ball valve of such type is in controlling the flow of a refrigerant through a refrigeration system, such as may be used in a grocery store, storage facility, or like location. Refrigeration systems in such locations may employ multiple refrigerators linked to a common refrigerant source and common or connected flow pathways. Ball valves may be used to control a flow of refrigerant through the system among the individual refrigerators. A ball valve, for example, typically is provided at the inlet and outlet of a refrigerated display case.
In many applications that employ isolation valves, and ball valves in particular, pressure build-up in the fluid system can give rise to safety concerns. This concern can be particularly pronounced in refrigeration systems that operate at high pressure, especially for example in systems in which carbon dioxide is the refrigerant. When closed, the ball valve stops the flow of refrigerant in the system. Trapped refrigerant can warm up while the ball valve is closed, which can cause pressure in the system to build leading to a potentially unsafe condition This issue is particularly acute with carbon dioxide refrigerant because a small change in temperature results in a substantial spike in pressure.
To address the safety issue associated with pressure build-up, ball valve assemblies may be provided with pressure relief features. Conventional ball valve assemblies utilize two valves to relieve the pressure. In such systems, a ball valve and a check valve are typically piped in parallel with one another, with the check valve bleeding off excess pressure. This conventional configuration employing multiple, parallel pathways typically includes several joints that must be brazed together. The conventional configuration is therefore deficient in that the need for several joints brazed together increases the size and number of components in the ball valve assembly, thereby increasing cost and providing for less efficient functioning of the ball valve than is desirable.